Jedlitschky G, Huber M, Völkl A, Müller M, Leier I, Müller J, Lehmann W D, Fahimi H D, Keppler D
Deutsches Krebsforschungszentrum, Heidelberg, Federal Republic of Germany.
J Biol Chem. 1991 Dec 25;266(36):24763-72.
Chain shortening via beta-oxidation from the omega-end has been recognized as the major pathway for the degradation of cysteinyl leukotrienes as well as leukotriene B4 (LTB4). The metabolic compartmentation of this pathway was studied using peroxisomes purified from normal and clofibrate-treated rat liver. beta-Oxidation products of omega-carboxy-LTB4, including omega-carboxy-dinor-LTB4 identified by gas chromatography-mass spectrometry, were formed by the isolated peroxisomes. The reaction was dependent on CoA, ATP, and NAD and was stimulated by FAD. NADPH was necessary for the further metabolism of omega-carboxy-dinor-LTB4. Together with microsomes a degradation of omega-carboxy-LTB4 also proceeded in isolated mitochondria in the presence of CoA, ATP, and carnitine. beta-Oxidation of the cysteinyl leukotriene omega-carboxy-N-acetyl-leukotriene E4 was observed only with isolated peroxisomes in combination with lipid-depleted microsomes. Direct photoaffinity labeling using omega-carboxy-[3H] LTB4 and omega-carboxy-N-[3H]acetyl-LTE4 served to identify peroxisomal leukotriene-binding proteins. The bifunctional protein (EC 4.2.1.17 and 1.1.1.35) and 3-ketoacyl-CoA thiolase (EC 2.3.1.16) of the peroxisomal beta-oxidation system were the predominantly labeled polypeptides as revealed by precipitation with monospecific antibodies. In vivo studies with N-acetyl-[3H2]LTE4, N-acetyl-[3H8]LTE4, and N-[14C]acetyl-LTE4 after treatment with the peroxisome proliferator clofibrate indicated formation and biliary excretion of large amounts of metabolites more polar than omega-carboxy-tetranor-N-acetyl-LTE3 including omega-carboxy-tetranor-delta 13-N-acetyl-LTE4 and omega-carboxy-hexanor-N-acetyl-LTE3. Increased formation of beta-oxidized catabolites of N-acetyl-LTE4 and LTB4 was also observed in hepatocytes isolated after clofibrate treatment. Our results indicate that peroxisomes play a major role in the beta-oxidation of leukotrienes from the omega-end. Whereas omega-carboxy-LTB4 was beta-oxidized both in isolated peroxisomes and mitochondria, the cysteinyl leukotriene omega-carboxy-N-acetyl-LTE4 was exclusively degraded in peroxisomes.
从ω端通过β-氧化进行的链缩短已被公认为是半胱氨酰白三烯以及白三烯B4（LTB4）降解的主要途径。使用从正常和氯贝丁酯处理的大鼠肝脏中纯化的过氧化物酶体研究了该途径的代谢区室化。ω-羧基-LTB4的β-氧化产物，包括通过气相色谱-质谱法鉴定的ω-羧基-去甲-LTB4，由分离的过氧化物酶体形成。该反应依赖于辅酶A、ATP和NAD，并受到FAD的刺激。NADPH是ω-羧基-去甲-LTB4进一步代谢所必需的。在辅酶A、ATP和肉碱存在的情况下，分离的线粒体与微粒体一起也能使ω-羧基-LTB4发生降解。仅在分离的过氧化物酶体与脂质缺乏的微粒体结合时，才观察到半胱氨酰白三烯ω-羧基-N-乙酰白三烯E4的β-氧化。使用ω-羧基-[3H]LTB4和ω-羧基-N-[3H]乙酰-LTE4进行直接光亲和标记，以鉴定过氧化物酶体白三烯结合蛋白。过氧化物酶体β-氧化系统的双功能蛋白（EC 4.2.1.17和1.1.1.35）和3-酮酰基辅酶A硫解酶（EC 2.3.1.16）是主要的标记多肽，这通过用单特异性抗体沉淀得以揭示。在用过氧化物酶体增殖剂氯贝丁酯处理后，对N-乙酰-[3H2]LTE4、N-乙酰-[3H8]LTE4和N-[14C]乙酰-LTE4进行的体内研究表明，形成并经胆汁排泄了大量比ω-羧基-四去甲-N-乙酰-LTE3极性更强的代谢产物，包括ω-羧基-四去甲-δ13-N-乙酰-LTE4和ω-羧基-六去甲-N-乙酰-LTE3。在氯贝丁酯处理后分离的肝细胞中，也观察到N-乙酰-LTE4和LTB4的β-氧化分解产物形成增加。我们的结果表明，过氧化物酶体在白三烯从ω端的β-氧化中起主要作用。虽然ω-羧基-LTB4在分离的过氧化物酶体和线粒体中都能进行β-氧化，但半胱氨酰白三烯ω-羧基-N-乙酰-LTE4仅在过氧化物酶体中降解。
